Though Bernard of Clairvaux shared bread of vetch meal with his monks during the famine of 1124-26,[Note 1] an emblem of humility, eventually the Bitter Vetch was dropped from human use, save as a crop of last resort in times of starvation: vetches "featured in the frugal diet of the poor until the eighteenth century, and even reappeared on the black market in the South of France during the Second World War", Maguelonne Toussaint-Samat, of Marseillais background, has remarked.[4] Broad beans remained prominent though, be it in the Near East where the seeds are mentioned in Hittite and Ancient Egyptian sources dating from more than 3,000 years ago as well as in the Hebrew Bible,[Note 2] or in the large CelticOppidum of Manching from La Tène Europe some 2,200 years ago. Dishes resembling ful medames are attested in the Jerusalem Talmud which was compiled before 400 AD.

The vetches grown as forage are generally toxic to non-ruminants (such as humans), at least if eaten in quantity. Cattle and horses have been poisoned by V. villosa and V. benghalensis, two species that contain canavanine in their seeds. Canavanine, a toxic analogue of the amino acid arginine, has been identified in Hairy Vetch as an appetite suppressant for monogastric animals, while Narbon bean contains the quicker-acting but weaker γ-glutamyl-S-ethenylcysteine.[10] In common vetch, γ-glutamyl-β-cyanoalanine has been found. The active part of this molecule is β-cyanoalanine. It inhibits the conversion of the sulfur amino acid methionine to cysteine.

Cystathionine, an intermediary product of this biochemical pathway, is secreted in urine.[11] This process can effectively lead to the depletion of vital protective reserves of the sulfur amino acid cysteine and thereby making Vicia sativa seed a dangerous component in mixture with other toxin sources. The Spanish pulse mix comuña contains common vetch and bitter vetch in addition to vetchling (Lathyrus cicera) seeds; it can be fed in small quantities to ruminants, but its use as a staple food will cause lathyrism even in these animals. Moreover, common vetch as well as broad bean – and probably other species of Vicia too – contain oxidants like convicine, isouramil, divicine and vicine in quantities sufficient to lower glutathione levels in G6PD-deficient persons to cause favism disease. At least broad beans also contain the lectinphytohemagglutinin and are somewhat poisonous if eaten raw. Split common vetch seeds resemble split red lentils (Lens culinaris), and has been occasionally mislabelled as such by exporters or importers to be sold for human consumption. In some countries where lentils are highly popular – e.g., Bangladesh, Egypt, India and Pakistan – import bans on suspect produce have been established to prevent these potentially harmful scams.[10][12]

^"Their bread like the prophets of old, was made of barley, millet and vetch and was of such miserable quality that once a visiting monk, lamenting sadly their plight, took away with him some of what had been set before him in the guest-house, that he might show to everybody the marvel of men, and such men, living on the like." (Vita Prima I.v.25, quoted in Williams (1952), p. 24).[3]

^Usually translated simply as "beans"; the green beans (Phaseolus) are native to the Americas and were unknown in Europe before about 1500 AD.